The latest rumor suggests that Apple is tentatively planning to unveil the iPhone 6 in mid-September. With the iPhone 4s having launched in early October, and the iPhone 5 and iPhone 5s hitting in subsequent Septembers, mid-September 2014 certainly seems fairly likely for the iPhone 6. As per 9to5Mac:
[According to sources briefed on the plans,] the second and third weeks of September are the mostly likely weeks for the event to be held, but they add that manufacturing uncertainties could alter the event's timeframe. A decision has not been finalized, and sources made it clear that the plans are in flux.
Mid-September makes sense for when we'll see the iPhone 6, the shipping version of iOS 8, and whatever else it is that Apple has up their sleeves for that day, and is pretty much in line with what iMore speculated back in January. However, it's important to remember that nothing is set in stone until Apple sends out invitations.
In line with other iPhone 6 rumors, there's reportedly some indecision on Apple's part is on whether or not to announce the larger 5.5-inch iPhone alongside the 4.7-inch model (which is apparently "farther along in both internal testing and manufacturing preparation", which also lines up with the bulk of reports), or to push that one back and launch just the smaller (but yet bigger) version.
Regardless of whether the iPhone 6 launches in September or October or May, what are you most looking forward to?